Such a conventional inner fin with cutout window for heat exchanger is disclosed in, for example, Japanese Patent No. 2555449. In this conventional inner fin, a flat plate having a plurality of rectangular holes bored therein is folded in a rectangular corrugated shape, so that vertical walls and lateral walls are formed in a rectangular shape to extend continuously along the flow direction of a heat exchange medium, and a slit is formed to run along each of the vertical walls to part of the lateral walls on both sides of the vertical wall. The vertical walls and the lateral walls split the flow of the heat exchanging medium into their wall directions, and the slits allow theses split heat exchanging mediums to flow through the slits and partially mix up with each other, thereby generating the turbulence to inhibit the development of boundary layers on their walls.
However, the conventional inner fin described above has the following problem. The vertical walls and the lateral walls are formed in the rectangular shape folding to extend step-free along the flow direction of the heat exchange medium with the slits interposed therebetween. This structure can reduce pressure loss caused by a flow of the heat exchange medium in the conventional inner fin compared with that in an offset inner fin, while only small split flow of the heat exchange medium occurs from one passage to another through the slits. This reason comes from that the vertical walls and the lateral walls, as the whole structure, continuously extend step-free along the flow direction of the heat exchange medium, which makes the heat exchange medium to flow in parallel through front and rear side passages on both sides of the vertical walls at an equal speed. This brings only a small split flow through the slit to a passage to its adjacent passage, therefore, the effect of improving heat exchange efficiency has been still small.
Moreover, protruding ridges extend continuously in a width direction of the plate, and therefore, in order to obtain the passages of the heat exchange medium longer than one plate, a plurality of plates each having protruding ridges similarly to the above plate have to be arranged in the width direction and connected with adjoining plates to form one inner fin, which has led to increase in production cost.
The present invention was made in view of the problems stated above, and an object thereof is to provide a low cost inner fin with cutout window for heat exchanger that can reduce pressure loss of a heat exchange medium in a heat exchanger such as a condenser and achieve a high effect of improving heat exchange efficiency.